1. Field of the Invention
The present invention relates to an optical apparatus configured to perform an automatic focusing (AF) operation, an imaging apparatus including the optical apparatus, and a method for controlling the optical apparatus or the imaging apparatus.
2. Description of the Related Art
There are conventional optical systems which can generate a sound or visual output indicating an in-focus determination result when a user presses a shutter button in a still image shooting mode.
For example, as discussed in Japanese Patent Application Laid-Open No. 6-205258, an in-focus position detection apparatus enables a user to confirm an in-focus position displayed on a screen of a viewfinder. This apparatus determines a specific block corresponding to an in-focus position based on a comparison of high-frequency components in respective blocks between the image signals of two successive pictures. Then, the apparatus blinks the identified in-focus block on the screen of the viewfinder.
Furthermore, as discussed in Japanese Patent Application Laid-Open No. 2004-333828, there is an imaging apparatus including an indicator that notifies a user about the degree of an in-focus state. This apparatus quantitatively calculates a focusing degree of each image received via an image-pickup lens and generates a sound or visual output indicating the detected focusing degree.
Moreover, as another conventional technique, a hybrid AF system including a TV-AF system and another focus detection system (e.g., a phase-difference AF system) can speedily and accurately perform a focusing operation.
A focus adjustment based on the TV-AF system includes processes of obtaining a video signal from an image sensor that applies a photoelectric conversion to an object image, extracting a high-frequency component (i.e., an AF evaluation value) from the video signal obtained by the image sensor via a band-pass filter, and searching for a position where the AF evaluation value can be maximized while a focusing lens is moved.
On the other hand, a focus adjustment based on the phase-difference AF system includes processes of splitting incident light from an object into two focus detection sensors which are separately provided, detecting a deviation of output images of the sensors, and calculating an object distance based on the detected deviation according to the principle of triangulation.
According to the above-described hybrid AF system, a detection object area (e.g., a range-finding area or in-focus detection area) of one AF system tends to be different from a detection object area of the other AF system.
Hence, as discussed in Japanese Patent Application Laid-Open No. 2002-311328, an electronic camera can be configured to notify a user about a detection object area and an in-focus determination result when a user presses a shutter button, so that the user can easily focus the electronic camera on a desired object.
However, according to the focus adjustment based on the conventional TV-AF system, the moving direction of the focusing lens is repeatedly reversed to search for a target position where the AF evaluation value can be maximized. The apparatus cannot determine that the focusing lens has reached an in-focus state before the focusing lens comes to repeatedly continue reversing motions. Therefore, a relatively long time is required until a user is notified about an in-focus state of the focusing lens. The user may feel a sense of discomfort.
In particular, the above-described hybrid AF system discussed in Japanese Patent Application Laid-Open No. 2002-311328 first performs a rough focusing control based on the phase-difference AF system and then performs a precise focusing control based on the TV-AF system to finally move the focusing lens to a target (i.e., in-focus) position. In other words, it takes a long time to finally determine an in-focus state of the focusing lens, and the notification to a user is significantly delayed.